Liquid crystal displays having advantages over small size, light weight, and low power consumption are widely applied to various types of electronic products. In order to achieve high-precision components and pixel arrangement degrees, low-temperature polysilicon (LTPS) thin-film transistor liquid crystal displays have become the mainstream of development.
However, low-temperature polysilicon has a problem that the conventional low-temperature polysilicon thin film transistor (LTPS-TFT) structure comprises two n-doped regions formed on a polysilicon layer as a source and a drain. Since a doping concentration of the two n-doped regions is higher and a distance between the gate electrode and the n-doped region is very small, a strong electric field closing to the drain causes a hot carrier effect. Thus, a leakage current will occur while the polysilicon thin film transistor is in the OFF state. To solve this problem, the conventional technology uses a lightly doped drain (LDD) structure to reduce the electric field which is in contact with the drain and thus reduce the leakage current. Referring to FIG. 1, in the process of manufacturing a conventional low-temperature polysilicon thin film transistor, the formation of a self-aligned lightly doped drain structure thin film transistor array substrate as below: 1. forming a buffer layer 11 and a non-polysilicon layer on a substrate 10, the non-polysilicon layer crystallized into a polysilicon layer 12 by an excimer laser annealing process, and defining a polysilicon region by a mask; 2. defining a n-doped region by the mask and performing a ion-implantation process to implant ions to form the n-doped region; 3. forming a gate insulating layer 14 on the polysilicon layer 12 by a plasma-enhanced chemical vapor deposition process; 4. forming a gate 15 on the gate insulating layer 14, and defining a gate region by the mask, etching other metal by a dry etching process; 5. performing the ion-implantation process (shown by the arrow in FIG. 1) and using the gate 15 as the mask to form a lightly doped drain region 16.
By etching the gate with the dry etching process, the gate insulating layer will also be etched and the gate insulating layer will be lost. While performing the ion-implantation process to form the lightly doped drain region, the ions implanted into the polysilicon layer will cause the dosage of the ions to be uneven. Thus, the electric properties of each where of the a channel of the thin-film transistor produces differences and results in the brightness of liquid crystal display being uneven or dark spots may occasionally appear on the liquid crystal display.